java - 如何使用 Jackson 反序列化动态 JSON 字段？

Question

如何将具有动态字段(如下面代码中称为故事的对象)的 JSON 对象反序列化为对象数组？

{
   stories: {
      -IhO1742Lki-Pit0snot: {
         sentences: {
            -IhO2fyAEn15XUge6HeY: {
               userName: "Giulia",
               text: "a dude created a new religion called PornDora"
            },
            -IhO2fyAEn15XUge6HeZ: {
               userName: "Will",
               text: "but it was kidnapped by a flying burrito copter"
            },
            -IhO2fyAEn15XUge6HeX: {
               userName: "Jasmine",
               text: "I went this morning at AngelHack hackaton"
            }
         }
      },
      -IhO-gNvUPHpB9fOn-Gm: {
         sentences: {
            -IhO0PBBnJavU2gfMcVO: {
               userName: "Giorgio",
               text: "I woke up alone in a dark alley and a yellow cat was starring at me"
            },
            -IhO11CWL9r6G4Pu8YXx: {
               userName: "Will",
               text: "the cat runned away when a blurred figure approached me and called my name"
            }
         }
      }
   }
}

下面是我用于反序列化的 Java 类:

public class Story {

    private String id;
    private List sentences;

    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id;
    }
    public List getSentences() {
        return sentences;
    }
    public void setSentences(List sentences) {
        this.sentences = sentences;
    }

}

public class Sentence {

    private String id;
    private String text;
    private String userName;



    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id;
    }
    public String getText() {
        return text;
    }
    public void setText(String text) {
        this.text = text;
    }
    public String getUserName() {
        return userName;
    }
    public void setUserName(String userName) {
        this.userName = userName;
    }

}

Answer 1

您是否控制 JSON 序列化的格式？例如，您能否改用以下格式:

{
    "stories": [
        {
            "id": "-IhO1742Lki-Pit0snot", 
            "sentences": [
                {
                    "id": "-IhO2fyAEn15XUge6HeY", 
                    "text": "a dude created a new religion called PornDora", 
                    "userName": "Giulia"
                }
            ]
        )
    ]
}

如果您控制序列化方面，您可以尝试使用 Polymorphic Type Handling (PTH)。

这将为 Jackson 提供足够的类型信息来反序列化您的对象。

另见 Tatu 的 accompanying blog post了解背景信息。

---

这是 Jackson 1.x 中 PTH 的代码片段。如果你想使用 Jackson 2.x，你将利用 com.fasterxml packages并且需要稍微更改代码。

// import com.fasterxml.jackson.annotation.JsonTypeInfo;
// import com.fasterxml.jackson.databind.ObjectMapper;
import org.codehaus.jackson.annotate.JsonTypeInfo;
import org.codehaus.jackson.map.ObjectMapper;

public class MyObjectMapperProvider {
    final ObjectMapper defaultObjectMapper;

    public MyObjectMapperProvider() {
        System.out.println("MyObjectMapperProvider()");


        this.defaultObjectMapper = new ObjectMapper();
        this.defaultObjectMapper.enableDefaultTyping(
            ObjectMapper.DefaultTyping.NON_FINAL, JsonTypeInfo.As.WRAPPER_OBJECT
        );
        // .enableDefaultTyping();
        // .enableDefaultTyping(ObjectMapper.DefaultTyping.OBJECT_AND_NON_CONCRETE);
        // .enableDefaultTyping(ObjectMapper.DefaultTyping.NON_FINAL, JsonTypeInfo.As.WRAPPER_OBJECT); 
        // this.defaultObjectMapper.addMixInAnnotations(Bindable.class, MyObjectMapperProvider.MixIn.class);
        // this.defaultObjectMapper.addMixInAnnotations(DataModel.WriteOp.class, MyObjectMapperProvider.MixIn.class);
    }
}

---

顺便说一下，您提供的 json 实际上不是有效的 JSON。尝试使用

   {
        "stories": {
            "-IhO-gNvUPHpB9fOn-Gm": {
                "sentences": {
                    "-IhO0PBBnJavU2gfMcVO": {
                        "text": "I woke up alone in a dark alley and a yellow cat was starring at me", 
                        "userName": "Giorgio"
                    }, 
                    "-IhO11CWL9r6G4Pu8YXx": {
                        "text": "the cat runned away when a blurred figure approached me and called my name", 
                        "userName": "Will"
                    }
                }
            }, 
            "-IhO1742Lki-Pit0snot": {
                "sentences": {
                    "-IhO2fyAEn15XUge6HeX": {
                        "text": "I went this morning at AngelHack hackaton", 
                        "userName": "Jasmine"
                    }, 
                    "-IhO2fyAEn15XUge6HeY": {
                        "text": "a dude created a new religion called PornDora", 
                        "userName": "Giulia"
                    }, 
                    "-IhO2fyAEn15XUge6HeZ": {
                        "text": "but it was kidnapped by a flying burrito copter", 
                        "userName": "Will"
                    }
                }
            }
        }
    }

您可以通过将其传递到 python -m json.tool 来验证您的 json 是否正确。在 OS X 上，您可以将 json 复制到剪贴板并将其传递给 json.tool，如下所示:

 > pbpaste | python -m json.tool

---

如果您想尝试一下，这里有一个利用 Jersey 的小例子。使用 curl http://localhost:7654/sandbox/test 来练习一下:

主类.java

import java.net.URI;

import org.glassfish.grizzly.http.server.HttpServer;
// import org.glassfish.hk2.utilities.binding.AbstractBinder;
import org.glassfish.jersey.grizzly2.httpserver.GrizzlyHttpServerFactory;
import org.glassfish.jersey.jackson.JacksonFeature;
import org.glassfish.jersey.server.ResourceConfig;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class MainClass {
     private static final Logger LOG = LoggerFactory.getLogger(MainClass.class);
     public static final String PATH = "http://localhost:7654/sandbox/";
     public static void main(String[] args) {
          // create a resource config that scans for JAX-RS resources and providers
          // in com.mlbam.monitoring.lsg.data_aggregator package
          final ResourceConfig rc = new ResourceConfig()
                .packages("com.mlbam.internal")
                // .packages("com.mlbam.monitoring.collector.provis")
                .register(MyObjectMapperProvider.class)
                .register(JacksonFeature.class)
          ;

          // create and start a new instance of grizzly http server
          // exposing the Jersey application at BASE_URI
          final HttpServer grizzlyServerV1 = GrizzlyHttpServerFactory.createHttpServer(URI.create(PATH), rc);
          LOG.info("Jersey app started with WADL available at {}application.wadl", PATH);
          try {
                Thread.sleep(10_000);
          } catch (InterruptedException e) { }
          LOG.info("Stopping");
     }
}

MyObjectMapperProvider.java:

// import com.fasterxml.jackson.annotation.JsonTypeInfo;
// import com.fasterxml.jackson.databind.ObjectMapper;
import org.codehaus.jackson.annotate.JsonTypeInfo;
import org.codehaus.jackson.map.ObjectMapper;

import javax.ws.rs.ext.ContextResolver;
import javax.ws.rs.ext.Provider;

@Provider
public class MyObjectMapperProvider implements ContextResolver<ObjectMapper> {
    final ObjectMapper defaultObjectMapper;

    public MyObjectMapperProvider() {
         System.out.println("MyObjectMapperProvider()");

         this.defaultObjectMapper = new ObjectMapper();
         this.defaultObjectMapper.enableDefaultTyping(
               ObjectMapper.DefaultTyping.NON_FINAL, JsonTypeInfo.As.WRAPPER_OBJECT
         );
         // .enableDefaultTyping();
         // .enableDefaultTyping(ObjectMapper.DefaultTyping.OBJECT_AND_NON_CONCRETE);
         // .enableDefaultTyping(ObjectMapper.DefaultTyping.NON_FINAL, JsonTypeInfo.As.WRAPPER_OBJECT); 
         // this.defaultObjectMapper.addMixInAnnotations(Bindable.class, MyObjectMapperProvider.MixIn.class);
         // this.defaultObjectMapper.addMixInAnnotations(DataModel.WriteOp.class, MyObjectMapperProvider.MixIn.class);
    }

    @Override
    public ObjectMapper getContext(Class<?> type) {
         System.out.println("MyObjectMapperProvider.getContext(" + type + ")");
         return this.defaultObjectMapper;
    }


    // @JsonTypeInfo(use=JsonTypeInfo.Id.CLASS, include=JsonTypeInfo.As.PROPERTY, property="@class")
    // public static class MixIn {
    // }
}

我的资源.java

import javax.inject.Singleton;

import javax.ws.rs.core.Response;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;

@Singleton
@Path("test/")
public class MyResource {
    // public Thing[] state = {new Thing("asdf"), new Thing("foo"), new Thing("bar")};
    public String[] state = {"asdf", "foo", "bar"};

    @GET
    @Produces(MediaType.APPLICATION_JSON)
    public Response test() {
         return Response.ok(state).build();
    }
}

依赖关系(如果使用 maven):

<dependencies>
    <!-- Logging -->
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-api</artifactId>
        <version>1.7.5</version>
    </dependency>
    <dependency>
        <groupId>ch.qos.logback</groupId>
        <artifactId>logback-classic</artifactId>
        <version>1.0.13</version>
    </dependency>
    <dependency>
        <groupId>ch.qos.logback</groupId>
        <artifactId>logback-core</artifactId>
        <version>1.0.13</version>
    </dependency>
    <!-- Jersey Specific Dependencies -->
    <dependency>
        <groupId>org.glassfish.jersey.containers</groupId>
        <artifactId>jersey-container-grizzly2-http</artifactId>
        <version>2.3.1</version>
    </dependency>
    <dependency>
        <groupId>org.glassfish.jersey.media</groupId>
        <artifactId>jersey-media-json-jackson</artifactId>
        <version>2.3.1</version>
    </dependency>
</dependencies>